Catalyst composition and method for producing diaryl carbonates using nitrile as promoter

ABSTRACT

Hydroxyaromatic compounds such as phenol are carbonylated with oxygen and carbon monoxide in the presence of a catalyst system comprising a Group VIIIB metal, preferably palladium; an alkali metal or alkaline earth metal halide, preferably sodium bromide; and a promoter compound which is at least one C 2-8  aliphatic or C 7-10  aromatic mono- or dinitrile, preferably acetonitrile or adiponitrile. The catalyst system also preferably contains a compound of a non-Group VIIIB metal, preferably lead.

This application is a divisional of Ser. No. 09,345,538 filed Jun. 30,1999.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of diaryl carbonates byoxidative carbonylation. More particularly, it relates to theimprovement of diaryl carbonate yield in the carbonylation reaction.

Diaryl carbonates are valuable intermediates for the preparation ofpolycarbonates by transesterification with bisphenols in the melt. Thismethod of polycarbonate preparation has environmental advantages overmethods which employ phosgene, a toxic gas, as a reagent andenvironmentally detrimental chlorinated aliphatic hydrocarbons such asmethylene chloride as solvents.

Various methods for the preparation of diaryl carbonates by an oxidativecarbonylation (hereinafter sometimes simply “carbonylation” for brevity)reaction of hydroxyaromatic compounds with carbon monoxide and oxygenhave been disclosed. In general, the carbonylation reaction requires arather complex catalyst. Reference is made, for example, to U.S. Pat.No. 4,187,242, in which the catalyst is a Group VIIIB metal, i.e., ametal selected from the group consisting of ruthenium, rhodium,palladium, osmium, iridium and platinum, or a complex thereof.

A further development in the carbonylation reaction, including the useof compounds of other metals such as lead or cerium as cocatalysts, isdisclosed in various patents including U.S. Pat. No. 5,498,789. Alsorequired according to that patent is the use of quaternary ammonium orphosphonium halides, as illustrated by tetra-n-butylammonium bromide, aspart of the catalyst package.

The commercial viability of the carbonylation reaction would be greatlyincreased if a less expensive compound could be substituted for thequaternary ammonium or phosphonium halide. It has been discovered,however, that substitution of such compounds as sodium bromide normallyresults in the isolation of the desired diaryl carbonate in low orinsignificant yield.

In U.S. Pat. Nos. 5,543,547 and 5,726,340, the use of carbonylationcatalyst systems including palladium or an analogous metal, variouscocatalytic metals which may include cerium, lead or cobalt, and analkali metal or quaternary ammonium bromide is disclosed. Also presentmay be materials characterized as inert solvents. These may be aliphaticor alicyclic hydrocarbons such as hexane, heptane or cyclohexane;chlorinated aliphatic hydrocarbons such as methylene chloride orchloroform; aromatic hydrocarbons such as toluene or xylene; chlorinatedaromatic hydrocarbons such as chlorobenzene; ethers such as diethylether, diphenyl ether, tetrahydrofuran or dioxane; esters such as ethylacetate or methyl formate; nitroaromatic compounds such as nitrobenzene;or acetonitrile. There is no suggestion, however, that yields of diarylcarbonate are in any way improved by the use of any of these “solvents”in a halide-containing catalyst package.

U.S. Pat. No. 5,380,907 discloses the use of a nitrile in combinationwith palladium and a manganese or copper cocatalyst. The result is anincrease in yield, but yields are still too low to permit contemplationof commercial use for the disclosed catalyst systems.

It is of interest, therefore, to develop catalyst systems which includean inexpensive halide compound and which can efficiently produce diarylcarbonates.

SUMMARY OF THE INVENTION

The present invention provides a method for preparing diaryl carbonateswhich includes a relatively inexpensive halide and a promoter compoundwhich maximizes the effectiveness of said halide. Also provided is acatalyst composition useful in such a method.

In one of its aspects, the invention is a method for preparing a diarylcarbonate which comprises contacting at least one hydroxyaromaticcompound with oxygen and carbon monoxide in the presence of an amounteffective for carbonylation of at least one catalytic materialcomprising:

(A) a Group VIIIB metal or a compound thereof,

(B) at least one alkali metal halide, and

(C) an amount effective to optimize diaryl carbonate formation of apromoter compound which is at least one C₂₋₈ aliphatic or C₇₋₁₀ aromaticmono- or dinitrile.

Another aspect of the invention is catalyst compositions comprisingcomponents A, B and C as described above, and any reaction productsthereof.

DETAILED DESCRIPTION; PREFERRED EMBODIMENTS

Any hydroxyaromatic compound may be employed in the present invention.Monohydroxyaromatic compounds, such as phenol, the cresols, the xylenolsand p-cumylphenol, are generally preferred with phenol being mostpreferred. The invention may, however, also be employed withdihydroxyaromatic compounds such as resorcinol, hydroquinone and2,2-bis(4-hydroxyphenyl)propane or “bisphenol A”, whereupon the productsare polycarbonate oligomers.

Other essential reagents in the method of this invention are oxygen andcarbon monoxide, which react with the phenol to form the desired diarylcarbonate. They may be employed in high purity form or diluted withanother gas such as nitrogen, argon, carbon dioxide or hydrogen whichhas no negative effect on the reaction.

For the sake of brevity, the constituents of the catalyst system aredefined as “components” irrespective of whether a reaction between saidconstituents occurs before or during the carbonylation reaction. Thus,the catalyst system may include said components and any reactionproducts thereof.

Component A of the catalyst system is one of the Group VIIIB metals,preferably palladium, or a compound thereof. Thus, useful palladiummaterials include elemental palladium-containing entities such aspalladium black, palladium/carbon, palladium/alumina andpalladium/silica; palladium compounds such as palladium chloride,palladium bromide, palladium iodide, palladium nitrate, palladiumacetate and palladium 2,4-pentanedionate; and palladium-containingcomplexes involving such compounds as carbon monoxide, nitrites andolefins. Preferred in many instances are palladium(II) salts of organicacids, most often C₂₋₆ aliphatic carboxylic acids, and palladium(II)salts of β-diketones. Palladium(II) acetate and palladium(II)2,4-pentanedionate are generally most preferred. Mixtures of theaforementioned palladium materials are also contemplated.

Component B is at least one alkali metal halide. The alkali metalbromides such as lithium bromide, sodium bromide and potassium bromideare preferred, with sodium bromide often being most preferred by reasonof its particular suitability and relatively low cost.

Component C is a promoter compound, said compound being at least oneC₂₋₈ aliphatic or C₇₋₁₀ aromatic mono- or dinitrile. Illustrativemononitriles are acetonitrile, propionitrile and benzonitrile;illustrative dinitriles are succinonitrile, adiponitrile andbenzodinitrile. Mononitriles are generally preferred, with acetonitrileand adiponitrile being most preferred.

It should be noted that contrary to the suggestion of some of the priorart identified hereinabove, the function of component C in the presentinvention is not simply that of a solvent. Rather, the nitrite is anactive catalyst constituent which improves the yield of the desireddiaryl carbonate.

In a highly preferred embodiment of the invention, there is also presentin the catalyst system (D) at least one cocatalyst which is a compoundof a non-Group VIIIB metal, preferably one which is soluble in theliquid phase under the reaction conditions. Numerous other metalcompounds are known in the art to be active as carbonylationcocatalysts, and any compound having such activity may be used accordingto the present invention provided an improvement in diphenyl carbonateproduction, usually yield, is achieved thereby.

Illustrative cocatalytic metals include cerium, titanium, cobalt,copper, zinc, manganese, iron and lead, which may be used singly or incombination. For the purposes of this invention the preferredcocatalysts are those containing metals other than Group VIII metals;that is other than iron, cobalt and nickel. More preferred are compoundsof lead, particularly when used alone or in combination with titanium orcerium compounds. It should be noted, however, that component C is noteffective to optimize diaryl carbonate formation for all possiblepermutations of component D; the combined effectiveness of the two forthis purpose may be determined by simple experimentation.

Examples of lead compounds which may be employed are lead oxides such asPbO and Pb₃O₄ ⁻; inorganic lead salts such as lead(II) nitrate; leadcarboxylates such as lead(II) acetate, lead(II)propionate and lead(IV)acetate; lead alkoxides and aryloxides such as lead(II) methoxide andlead(II) phenoxide; and lead salts of β-diketones such as lead(II)2,4-pentanedionate. Mixtures of the aforementioned lead compounds mayalso be employed. The preferred lead compounds are lead(II) oxide,lead(II) aryloxides and lead(II) 2,4-pentanedionate. The preferredcompounds of other metals are, for the most part, salts of β-diketonesand especially 2,4-pentanedionates.

In addition to the aforementioned reactants and catalyst system, it isstrongly preferred for a desiccant to be present in the reaction system.The preferred desiccants are non-reactive materials such as molecularsieves, as illustrated by 3-Ångstrom (hereinafter “3A”) molecularsieves. They are usually isolated from the other reactants, as bypresence in a basket mounted to a stirrer shaft or the like.

Component A is most often present in the amount of about 0.1-100,000ppm, preferably 1-1,000 ppm, of Group VIIIB metal based onhydroxyaromatic compound, and component B in the amount of about 1-2,000gram-atom of total metal per gram-atom of palladium in component A.Component D, when employed, is generally present in the amount of about1-100 gram-atoms of total metal per gram-atom of palladium in componentA.

The role of component C in the composition and method of the inventionis believed to be to increase the degree of dissociation and ionizationof the halide anion of component B, perhaps by forming a complex withthe cationic portion of said component, although the invention is in noway dependent on this or any other theory of operation. The amount ofcomponent C employed will be an amount effective to optimize diarylcarbonate formation, in general by increasing the yield of the desireddiaryl carbonate as evidenced, for example, by an increase in “turnovernumber”; i.e., the number of moles of diaryl carbonate formed pergram-atom of palladium present. This amount is most often about 1 pratby weight of component C per 1-15, preferably about 1-6, parts ofhydroxyaromatic compound.

The method of the invention is preferably conducted in a reactor inwhich the hydroxyaromatic compound and catalyst system are charged underpressure of carbon monoxide and oxygen and heated. The reaction pressureis most often within the range of about 1-500 and preferably about 1-150atm. Gas is usually supplied in proportions of about 2-50 mole percentoxygen with the balance being carbon monoxide, and in any event, themole percentage of oxygen used should be outside the explosion range forsafety reasons. The gases may be introduced separately or as a mixture.Reaction temperatures in the range of about 60-150° C. are typical. Inorder for the reaction to be as rapid as possible, it is preferred tosubstantially maintain the total gas pressure and partial pressure ofcarbon monoxide and oxygen, as described, for example, in U.S. Pat. No.99,734, until conversion of the hydroxyaromatic compound is complete.

The diaryl carbonates produced by the method of the invention may beisolated by conventional techniques. It is often preferred to form andthermally crack an adduct of the diaryl carbonate with thehydroxyaromatic compound, as described in U.S. Pat. Nos. 239,106 and5,312,955.

The method of the invention is illustrated by the following examples.Minor variations in reagent amounts from one example to another are notbelieved significant from the standpoint of yield.

EXAMPLES 1-4

A constant composition gas flow reactor system, as disclosed in theaforementioned U.S. Pat. No. 5,399,734, was charged in each example with61.1 g (649 mmol) of phenol, 4.9 mg of palladium (26 ppm based onphenol) as palladium(II) 2,4-pentanedionate, 205.4 mg of lead(II) oxide,650 equivalents (based on palladium) of sodium bromide and variousproportions of acetonitrile. Molecular sieves, 38 g, were placed in aperforated polytetrafluoroethylene basket mounted to the stir shaft ofthe reactor.

The reactor was sealed, pressurized to 89.8 atm with a mixture of 9.1mole percent oxygen and 90.9 mole percent carbon monoxide and stirred asits temperature was increased to 100° C. over 10 minutes. Furtheroxygen-carbon monoxide mixture was introduced at a flow rate of 330ml/min and a pressure of about 88.5-89.8 atm. Gas flow was continued for2.5 hours, during which the reaction mixture was frequently analyzed byhigh pressure liquid chromatography.

The results are given in Table I, in comparison with eight controls.Turnover numbers are those observed at the point of highest diphenylcarbonate content of each reaction mixture, as shown by analysis.

TABLE 1 Phenol: Component C component C Component or replacement (orreplacement) Turnover Example B identity wt. ratio number 1 NaBrAcetonitrile 11.5 900 2 NaBr Acetonitrile 5.25 2216  3 NaBr Acetonitrile3.17 2992  4 NaBr Acetonitrile 1.08 2898  Control 1 TEAB — — 5587 Control 2 TEAB Acetonitrile 2.81 4130  Control 3 NaBr — — 626 Control 4— Acetonitrile 2.83 385 Control 5 NaBr Toluene 2.33 385 Control 6 NaBrChlorobenzene 2.23 375 Control 7 NaBr Diphenyl ether 2.45 535 Control 8NaBr Heptane 2.45 760

It can be seen that the proportion of diphenyl carbonate produced, asshown by turnover number, is substantially higher for Examples 1-4 thanfor Controls 3 and 4 in which components C and B, respectively, were notemployed, and also higher than for Controls 5-8 in which various othercompounds, including aliphatic and aromatic hydrocarbons, chlorinatedhydrocarbons and ethers, were employed in place of nitriles as componentC. In fact, the results of Examples 1-4 are comparable in certainrespects to Control 1, employing TEAB alone.

A comparison of Controls 1 and 2 shows that with TEAB, the presence ofacetonitrile results in a decrease in turnover number, contrary to thecomparison of Control 3 with Examples 1-4. Thus, it is unexpected andunpredictable that nitrites function as true promoters, not merely assolvents, when employed with sodium bromide.

EXAMPLE 5

The procedure of Examples 1-4 was repeated, omitting the lead(II) oxide.The results are given in Table II, in comparison with two controls.

TABLE II Phenol: component C Component C (or Component or replacementreplacement) Turnover Example B identity wt. ratio number 5 NaBrAcetonitrile 3.12 357 Control 9  TEAB — — 356 Control 10 NaBr — — 131

Table II shows that in the absence of component D, the use ofacetonitrile affords essentially the same results as the use of TEABwithout acetonitrile, and substantially superior results to the use ofsodium bromide without acetonitrile.

EXAMPLE 6

The procedure of Examples 1-4 was repeated, employing palladium(II)2,4-pentanedionate at a level of 17 ppm based on phenol, sodium bromideat a level of 230 equivalents based on palladium, a mixture of lead(II)oxide and titanium(IV) oxide bis(2,4-pentanedionate) (57 and 4equivalents, respectively, based on palladium), a pressure of 108.8 atmand a reaction time of 1.5 hours. Diphenyl carbonate was obtained at aturnover number of 5010.

EXAMPLES 7-8

Batch carbonylation experiments were conducted in glass reactor vessels,employing palladium(II) 2,4-pentanedionate, sodium bromide andadiponitrile at levels of 0.2 mmol of palladium per liter, 240equivalents of sodium bromide per equivalent of palladium and 53.8% byvolume adiponitrile based on phenol. Various cocatalyst combinationswere employed as component D. The reaction vessels were pressurized to81.6 atm with a mixture of 91.7 mole percent carbon monoxide and 8.3mole percent oxygen and heated at 100° C. for 3 hours. The contents ofthe vessels were analyzed for diphenyl carbonate by vapor phasechromatography. The results are given in Table III. The abbreviation“acac” represents the 2,4-pentanedionate. Cocatalyst proportions are inmoles of metal per gram-atom of palladium. The controls contained nonitrile but were otherwise similar in content.

TABLE III Example Cocatalyst (moles) Turnover number 7 Cull(acac)₂ (10)1316 TilVO(acac)₂ (10) 8 PbO (24) 1081 Celll/(acac)₃ (10) Control 9 Cull(acac)₂ (10) 364 TilVO(acac)₂ (10) Control 10 PbO (24) 540Celll/(acac)₃ (10)

It can be seen that production of diphenyl carbonate using thesecocatalysts in combination with sodium bromide was also substantiallyimproved by the addition of the nitrile.

What is claimed is:
 1. A catalyst composition comprising the followingand any reaction products thereof: (A) a Group VIIIB metal or a compoundthereof, (B) at least one alkali metal or alkaline earth metal halide,and (C) at least one promoter compound which is a C₂₋₈ aliphatic or aC₇₋₁₀ aromatic mono- or dinitrile.
 2. A composition according to claim 1further comprising (D) at least one cocatalyst which is a compound of anon-Group VIIIB metal.
 3. A composition according to claim 1 wherein theGroup VIIIB metal in component A is palladium.
 4. A compositionaccording to claim 3 wherein component A is palladium(II) acetate orpalladium(II) 2,4-pentanedionate.
 5. A composition according to claim 2wherein component D is a compound of a metal other than a Group VIIImetal.
 6. A composition according to claim 5 wherein component D islead(II) oxide.
 7. A composition according to claim 1 wherein componentC is an alkali metal bromide.
 8. A composition according to claim 7wherein component B is sodium bromide.
 9. A composition according toclaim 1 wherein component C is acetonitrile.
 10. A catalyst compositioncomprising the following and any reaction products thereof: (A)palladium or a compound thereof, (B) sodium bromide, (C) acetonitrileand (D) at least one lead compound and optionally titanium or ceriumcompound.
 11. The composition according to claim 1 wherein a desiccantis also present.
 12. The composition according to claim 10 wherein adesiccant is also present.